Feline leukemia virus (FeLV) is a retrovirus consisting of three subgroups designated A, B, and C. The FeLV subgroups were identified initially by viral interference and cross-neutralization. Sarma & Log, Virology (1973) 54:160-169; see also, Russell & Jarrett, Int'l J. Cancer (1978) 21:768-778; and Jarrett (1980) in Feline Leukemia Virus--Developments in Cancer Research Vol. 4, Hardy et al., eds., Elsevier North Holland, Inc., pp. 473-479. Feline leukemia virus is discussed also in Jarrett & Russell, Int'l J. Cancer (1978) 21:466-472; Sarma et al., J. Nat'l Cancer Inst. (1978) 60:871-874; and Schaller & Olsen Infect. Immun. (1975) 12:1405-1510.
FeLV is infectious in cats. It is responsible for a number of diseases, including lymphoplastic or aplastic anemia, myelosuppression, thymic atrophy, and thrombocytopenia, as well as reproductive failure, e.g., abortion, fetal resorption, and stillbirths. Neoplastic manifestations of FeLV infection, such as lymphosarcoma, account for only a small portion of the morbidity and mortality caused by FeLV. FeLV infection in cats, however, also causes suppression of the immune system, thereby exposing the animal to opportunistic infections by a variety of microorganisms.
Vaccines have been developed for FeLV. See, e.g., U.S. Pat. No. 4,332,793 to Olson, U.S. Pat. No. 4,264,587 to Pedersen et al., U.S. Pat. No. 4,117,112 to Jarrett et al., U.S. Pat. No. 4,086,134 to Jarrett et al., U.S. Pat. No. 4,034,081 to Jarrett et al., U.S. Pat. No. 3,966,907 to Jarrett et al., and Belgian Patent Application R 64 417 DG to the University of Glasgow.
In particular, a FeLV vaccine may be prepared from inactivated FeLV virus and from envelope glycoprotein (gp70), the antigen with which it is thought protective antibody must react. Such viral material generally may be produced by culturing infected feline cell lines, but it has been impossible to predict whether a particular feline cell line will produce viral material of appropriate quality in quantities sufficient to be useful for commercial production of FeLV vaccines. Moreover, a cell line which satisfactorily produces viral material for a given strain of FeLV may not produce adequate protection against other strains or may produce viral material that for other reasons is ineffective in vaccine formulations.
Thus, there is a continuing need to develop new systems for producing FeLV viral material that can be used in formulating commercially useful FeLV vaccines. It should also be noted that FeLV viral material is useful in the preparation of diagnositic reagents, and thus, new cell lines for its production are needed for that purpose as well.